Solar Oven Lesson

1

Solar Oven Project

Objective

Follow simple instructions to build a box solar oven from materials like cardboard boxes and
aluminum foil and then improve on the design to build a second, more efficient oven.

Introduction

Many devices have been developed that use solar energy—light and heat emitted from the sun —
including solar panels, artificial photosynthesis, and solar ovens. Solar ovens can cook food,
pasteurize water, or even sterilize instruments using only the power of the sun. How does a solar
oven work? The simple answer is that it is designed to absorb more heat than it releases.

Figure 1, below, shows a picture of the type of efficient, easy-to-build solar oven that you will be
making and testing in this project. The oven is a box within a box. The inner box is covered with a
plastic window (made from a heavy plastic cooking bag available at most grocery stores). The
plastic window works like a greenhouse roof, allowing direct and reflected sunlight to pass into the
inner box, while retaining radiated heat.

Figure 1. This box-type solar oven is both easy-to-build and very inexpensive! (Image credits:

Solar Cookers International Network, 2006)

At the bottom of the inner box, there is a foil-covered shelf, painted black. The shelf serves two
purposes. First, it holds the cooking pot. Second (and more importantly) it acts as a "heat sink."
The shelf absorbs direct and reflected sunlight, which warms it. The shelf then radiates the heat,
and this radiant energy stays mostly trapped in the inner box and warms it. The plastic window
holds the heat in, as does the insulation of the air space (and newspaper) that is between the
inner box and the outer box.

The Procedure section of this project idea gives you step-by-step instructions on building a simple
box-type solar oven. To make this into a complete science fair project, you will need to choose
some aspect of the solar oven design to improve and test. Your choice should be based on your

2

Solar Oven Project

Objective

Follow simple instructions to build a box solar oven from materials like cardboard boxes and
aluminum foil and then improve on the design to build a second, more efficient oven.

Introduction

Many devices have been developed that use solar energy—light and heat emitted from the sun —
including solar panels, artificial photosynthesis, and solar ovens. Solar ovens can cook food,
pasteurize water, or even sterilize instruments using only the power of the sun. How does a solar
oven work? The simple answer is that it is designed to absorb more heat than it releases.

Figure 1, below, shows a picture of the type of efficient, easy-to-build solar oven that you will be
making and testing in this project. The oven is a box within a box. The inner box is covered with a
plastic window (made from a heavy plastic cooking bag available at most grocery stores). The
plastic window works like a greenhouse roof, allowing direct and reflected sunlight to pass into the
inner box, while retaining radiated heat.

Figure 1. This box-type solar oven is both easy-to-build and very inexpensive! (Image credits:

Solar Cookers International Network, 2006)

At the bottom of the inner box, there is a foil-covered shelf, painted black. The shelf serves two
purposes. First, it holds the cooking pot. Second (and more importantly) it acts as a "heat sink."
The shelf absorbs direct and reflected sunlight, which warms it. The shelf then radiates the heat,
and this radiant energy stays mostly trapped in the inner box and warms it. The plastic window
holds the heat in, as does the insulation of the air space (and newspaper) that is between the
inner box and the outer box.

The Procedure section of this project idea gives you step-by-step instructions on building a simple
box-type solar oven. To make this into a complete science fair project, you will need to choose
some aspect of the solar oven design to improve and test. Your choice should be based on your

3

background research, and on the experience gained from building the first oven. Build a second
oven that includes your design improvement, and make measurements to see if you have
improved the oven's performance. You can test your oven by: measuring the internal temperature
with an oven thermometer, or by timing how long it takes to boil a given amount of water in a
cooking pot. Do not worry about the oven catching fire. Paper burns at 233°C (451°F), and your
solar oven will not get that hot.

When you are finished, it would be fun to try using your solar cooker to make a meal. The "Solar
Cooking Hints" webpage listed in the Bibliography, below, has some suggestions. Generally it
takes about twice as long to cook food with a solar oven than in a conventional oven, so you will
need to plan ahead. Rice is a good first dish to try.

Terms and Concepts

●Solar energy

●Greenhouses

●Reflected light

●Heat sink

●Radiant energy

●Insulation

Questions

●What is radiant energy? How is it used in a box-type solar oven to heat it up?

●How hot does a typical box-type solar oven get?

●How hot does an oven need to be to cook food?

●Can a solar cooker work on a cloudy day?

●Why use a black cooking pot?

Bibliography

You can find a bunch of alternative solar oven plans on this webpage:

●Solar Cookers International Network. (n.d.). Build a Solar Cooker. Retrieved July 10, 2014.

You can find other information on how solar ovens work and how to use them on these webpages:

●Solar Cookers International Network. (n.d.). Solar Cooking Hint. Retrieved July 10, 2014.

●Aalfs, M. (n.d.). Principles of Solar Box Cooker Design. Solar Cookers International
Network. Retrieved July 10, 2014.

●Sponheim, T. (n.d.). Developing an Intuitive Feel for the Dynamics of Solar Cooking.
Retrieved July 10, 2014.

4

Materials and Equipment

●Cardboard boxes (4). You will be building two solar ovens, and each oven requires two
cardboard boxes. Here are some notes on picking out two cardboard boxes for making a
single solar oven:

○The inner box should have an opening of at least 38 cm × 38 cm, and be large
enough to hold the cooking pot that you intend to use. It should only be about 2.5 cm
taller than the cooking pot.

○The outer box should be larger all around, with at least 1.5 cm of airspace between
the two boxes on each side. It should also ideally be about 2.5 cm–5.0 cm taller than
the inner box.

○The distance between the two boxes does not have to be equal all the way around.

○Tip: Keep in mind that it is very easy to adjust the size of a cardboard box by cutting
and gluing it.

●Metric ruler or measuring tape

●Straightedge, such as a hard ruler

●Utility knife

●Large sheets of cardboard (2) for making the lid for each of the two solar ovens. Each sheet
must be approximately 8-16 cm larger than the opening of the inner box, when measuring
both dimensions.

●Metal coat hanger. This is to make a prop for the lids.

●Pair of pliers. This is for cutting and bending coat hanger.

●Sheets of cardboard (2) for making the shelf/heat sink for each of the two solar ovens. Each
sheet must be the same size as the bottom of the inner box.

●Sheets of newspaper (several)

●A small roll of aluminum foil

●Black tempera paint (at least 4 oz.). Make sure it is not "washable" tempera paint. This can
be purchased locally at crafts stores or through online suppliers such as Amazon.com.

●Small paint brush

●Elmer's white school glue (at least 8 oz.)

●Reynolds oven cooking bag, "turkey-size", or 47.5 cm × 58.5 cm, or 19" × 23-1/2" (2; you
will need one bag for each of the two solar ovens). Notes on the cooking bag:

○These are available in almost all supermarkets in the U.S.

○They are rated for 204°C (400°F) so they are perfect for solar cooking.

○They are not UV-resistant, thus they will become brittle and opaque over time and
may need to be replaced periodically.

○A sheet of glass can also be used, but this is more expensive and fragile, and does
not offer that much better cooking except on windy days.

5

●For testing your ovens under the same solar conditions, you will need oven thermometers
(2 identical ones) or shallow black cooking pots with covers (2 identical ones). Alternatively,
instead of oven thermometers you could use an infrared thermometer (only 1) with a laser
pointer so you can aim it accurately inside of the solar ovens, such as this one from
Amazon.com.

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools®, Amazon.com,
Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science
Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student
learning. If you have any comments (positive or negative) related to purchases you've made for science
projects from recommendations on our site, please let us know. Write to us at
scibuddy@sciencebuddies.org.

Experimental Procedure

This project follows the

Scientific Method. Review the steps before you begin.

Safety Note: The solar oven you will be building is designed to cook food or boil water. Just like
your kitchen oven, temperatures inside the solar cooker will be high enough to cause serious
burns. Use oven mitts and proper caution to avoid burning yourself. Also, be careful with the utility
knife when cutting cardboard to make the oven.

Building the Solar Oven Base

1. Fold the top flaps closed on the outer box and set the inner box on top. Trace a line around

the base of the inner box onto the top of the outer box, as shown in Figure 2, below.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 2. Set the inner box on top of the (closed) outer box and draw lines around the bottom of

inner box onto the top of the outer box.

6

2. Remove the inner box and, carefully using the utility knife, cut along this line to form a hole

in the top of the outer box, as shown in Figure 3, below.

a. Set aside the outer box for now—you will use it again in step 6.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 3. Carefully cut along the line you made in step 1 to make the outer box have an opening

that the inner box can fit inside of.

3. Decide how tall you want your oven (the inner box) to be. We recommend about 2.5

centimeters (cm) taller than your largest pot, and about 2.5 cm – 5.0 cm shorter than the
outer box. (Note that you can change the height of the outer box in step 6, below.) This way
there will be a space between the bottoms of the boxes once the cooker is assembled.

4. Carefully use the utility knife to slit the corners of the inner box down to the height you

decided on, as shown in Figure 4, below.

7

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 4. Cut the corners of the inner box down to the height you want the box to be (based on

step 3).

5. Cut the new, extended flaps completely off so that you are left with a box (without flaps) that

is the height you want your oven to be. To do this, it is easiest to carefully use a
straightedge (e.g., a hard ruler) and the utility knife or a pair of scissors.

a. Set the inner box aside for now — you will not do anything more to it until step 9.

6. If you need to make the outer box shorter, do it now.

a. Remember, you want the outer box to be about 2.5 cm – 5 cm taller than the inner

box.

b. If you need to change the height of the outer box, at each corner measure down to

the new height you want the box to be and then make a mark there, along the box's
edge. Then carefully use a straightedge and the utility knife or a pair of scissors to
cut the box between the marked spots on the edges. You should end up cutting the
box into two pieces as shown in Figure 5, below. Stack the pieces on top of each
other (with one going inside of the other) and tape or glue them back together to
make an intact outer box that is the correct height.

8

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 5. If you need to make the outer box be shorter, cut it into two pieces (one being the new

height you want the box to be) and then glue or tape them back together (sliding one box inside of

the other) to make an intact outer box that is the correct height.

7. Glue aluminum foil to the inside of the outer box, as shown in Figure 6, below.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 6. Glue aluminum foil to the inside of the outer box.

8. Place some wads of crumpled newspaper into the outer box, as shown in Figure 7, below,

so that when you set the inner box down inside the hole in the outer box, the cut edges of
the inner box are even with the perimeter of the outer box, as shown in Figure 8, below.
Also place wads of crumpled newspaper in the side spaces between the inner and outer
box — this will help insulate the oven.

9

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 7. Place some newspaper wads into the bottom of the outer box for the inner box to sit on

top of.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 8. When the inner box is placed inside of the outer box, there should be enough newspaper

wads to support the inner box so that its edges are even with the perimeter of the outer box.

9. Glue aluminum foil to the inside of the inner box.

10.With the inner box placed inside of the outer box, glue the top edge of the inner box to the

perimeter of the outer box where they touch, as shown in Figure 9, below.

a. Tip: You may need to use some tape to help hold the boxes together while the glue

hardens.

10

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 9. Place the aluminum foil-coated inner box inside the outer box and glue the two boxes

together.

11. Finally, make a shelf/heat sink inside the inner box. Cut a piece of cardboard the same size

as the bottom of the inner box. Glue aluminum foil to one side, as shown in Figure 10,
below. Paint the foil black using black tempera paint and allow it to dry, as shown in Figure
11, below.

a. Tip: To coat the aluminum foil well, apply multiple (2 or 3) thin coats of paint, letting

each coat dry before adding the next one.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 10. Make a piece of cardboard be the same size as the bottom of the inner box, and then

cover one side of the cardboard with aluminum foil.

11

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 11. Paint the aluminum foil-covered cardboard piece with black tempera paint. You may

need to use multiple, thin layers of paint.

12.Once the paint has dried, put the shelf/heat sink in the oven so that it rests on the bottom of

the inner box (black side up). The solar oven base is now finished and should look similar to
Figure 12, below.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 12. The completed solar oven base should look similar to this one.

Building the Solar Oven's Removable Lid

1. Take one of the large sheets of cardboard (that you will use for a lid) and set the solar oven

base on top of it (centered). Trace the outline of the base onto the lid, as shown in Figure
13, below.

12

a. Note: Be sure to orient the corrugations of the lid so that they go from left to right as

you face the oven so that later the prop may be inserted into the corrugations (see
Figure 22, below).

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 13. Trace around the bottom of the solar oven base onto one of the large sheets of

cardboard. (The traced lines are faint in this picture.)

2. Carefully use the utility knife and straightedge (i.e., hard ruler) to cut through one (of the

two) sides of the cardboard along the lines you drew. Then fold the cardboard down along
the cut edges to make short flaps for the lid. Also cut the corner flaps so that the lid's flaps
can all fold down neatly.

3. Glue the lid's corners to the lid's side flaps to make the lid, as shown in Figure 14, below.

You may want to use binder clips to hold the corners together while they glue, as shown in
Figure 15, below.

a. Note: Do not glue the lid to the box! You will need to remove it to move pots in and

out of the oven.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 14. Glue the lid's corners and flaps together to make the lid look similar to this one.

13

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 15. While gluing the lid's corners, you can use binder clips to hold the corners together

while the glue hardens.

4. When the lid is done gluing, make sure it fits on the solar oven base as expected, as shown

in Figure 16, below.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 16. The lid should fit snugly on the solar oven base.

5. To make the reflector flap, draw a line on the lid, forming a rectangle the same size as the

oven opening (inner box size). Cut around three sides and fold the resulting flap up to form
the reflector, as shown in Figure 17, below.

a. As you did in step 2, carefully use the utility knife to cut through one (of the two)

cardboard layers where you want the flap to fold. Be sure to cut on the inside of the
lid so that the cut makes the lid fold back the correct way (instead of folding inwards).

14

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 17. Cut the cardboard lid so that it has a flap that is the same size as the oven's (inner

box's) opening.

6. Glue aluminum foil to the inside of the flap you just cut out, as shown in Figure 18, below.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 18. Glue the aluminum foil to the lid's flap.

7. Next, turn the lid upside-down and glue the oven cooking bag in place, covering the flap's

opening, as shown in Figure 19, below.

a. Use the turkey-size oven bag (47.5 cm × 58.5 cm, or 19" × 23-1/2") applied as is,

i.e., without opening it up. This makes a double layer of plastic. The two layers tend
to separate from each other to form an airspace as the oven cooks. Be sure to glue
the bag closed on its open end to stop water vapor from entering the bag and
condensing.

b. Alternatively, you could cut any size oven bag open to form a flat sheet large enough

to cover the oven opening.

15

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 19. Glue the cooking bag to the underside of the lid, covering the flap's opening. (Note that

aluminum foil-coated flap is on the other side of the cooking bag in this picture.)

8. Make a lid prop by using a pair of pliers to bend a 30 cm piece of coat hanger wire as

shown in Figure 20, below. Tip: You can carefully cut a piece of coat hanger wire to be this
length by making a groove on it and then snapping it at the groove. Be careful handling the
wire because the cut edges will be sharp!

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 20. Bend a 30 cm piece of coat hanger wire to make a lid prop like this one.

9. Insert the lid prop into the lid's corrugations as shown in Figure 21, below, to hold the flap

up. Your solar oven's lid is now complete!

16

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 21. Completed solar oven lid, with the prop holding the flap up.

10.Once the glue dries, your solar oven is complete and ready for cooking. Once the lid is put

on the solar oven base, the completed solar oven should look similar to the one in Figure
22, below.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 22. Completed solar oven.

Testing the Solar Oven's Performance

You will now be testing the solar oven's performance. You can do this by testing how long it takes
to boil water or by measuring the temperature inside the oven after letting it heat up. When you

17

test the solar oven, be sure you test it on a sunny day when it is fairly warm outside (>10°C, or
>50°F) with the solar oven facing the direction of the sun.

1. Testing how long it takes to boil water: Pour a specific amount of water (such as 2 cups),

into a shallow, black cooking pot (you will need two identical ones later for testing two solar
ovens at once). Time how long it takes the solar oven to boil the water. In your lab
notebook, be sure to record how much water you used and how quickly the water boiled.
You may want to create a data table to record this information.

2. Measuring the temperature inside the solar oven: Either use an oven thermometer (you will

need two identical ones later for testing two solar ovens at once) or an infrared
thermometer to measure the temperature of the solar oven after you have let it warm for a
certain amount of time, such as 45 minutes. To use the oven thermometer, keep the
thermometer in the oven and then quickly open the oven and read the temperature (if you
are unable to read the temperature through the oven bag). To read the infrared
thermometer, quickly open the oven and use the thermometer to find the temperature of the
black shelf/heat sink.

a. In your lab notebook, be sure to record the temperature of the solar oven and what

method you used to take the temperature.

3. How well did your solar oven perform? Are you surprised by your results? Do you think you

could make it work even better?

Improving Efficiency

The solar oven you have built should cook fine during most of the solar season. To improve the
efficiency to be able to cook on more marginal days, or make the solar oven be more efficient
overall, modify your solar oven's design. Think about how you want to modify it and then build a
second solar oven using the modified design. Test the original solar oven and your modified solar
oven next to each other and see if your modified solar oven is more efficient than the original

1. Here are some ideas for modifying the solar oven's design to make it more efficient:

a. Make pieces of foiled cardboard the same size as the oven sides and place these in

the wall spaces.

b. Make a new reflector the size of the entire lid.

c. Make the shelf/heat sink using sheet metal, such as aluminum flashing. Paint this

black and elevate this off the bottom of the oven slightly with small cardboard strips.
Note that you will want to make the inner box a bit taller to accommodate the
elevated shelf.

d. For additional help on thinking about how to improve the basic solar oven design,

you may want to check out the Science Buddies' resource on Engineering Design
Process.

2. After you have built your second solar oven using the modified design, test both solar ovens

together by repeating the "Testing the Solar Oven's Performance" section of the Procedure
with both ovens at the same time.

18

a. Note that you will need two identical, shallow, black cooking pots if you are testing

how long it takes water to boil in the ovens. Likewise, you will need two identical
oven thermometers or one infrared thermometer if you are testing the temperature
inside the ovens.

i.If you are using two identical oven thermometers, check first to make sure that
both thermometers give the same reading using your kitchen oven. If the
readings are different, make sure that the difference is consistent, and then
use the difference to correct one of the readings so that the measurements
can be compared.

b. Place the solar ovens side-by-side when testing them so that the conditions are the

same for both ovens. Be sure that both solar ovens are receiving the same amount
of light (i.e., one should not be partly shaded).

3. Repeat step 2 at least two more times so that you have compared the two solar ovens in at

least three trials.

4. Compare your results for each solar oven. Did the new design perform better than the

original design? Are your results what you expected them to be? Do you think you could
improve the solar oven design to make it even more efficient?

19

background research, and on the experience gained from building the first oven. Build a second
oven that includes your design improvement, and make measurements to see if you have
improved the oven's performance. You can test your oven by: measuring the internal temperature
with an oven thermometer, or by timing how long it takes to boil a given amount of water in a
cooking pot. Do not worry about the oven catching fire. Paper burns at 233°C (451°F), and your
solar oven will not get that hot.

When you are finished, it would be fun to try using your solar cooker to make a meal. The "Solar
Cooking Hints" webpage listed in the Bibliography, below, has some suggestions. Generally it
takes about twice as long to cook food with a solar oven than in a conventional oven, so you will
need to plan ahead. Rice is a good first dish to try.

Terms and Concepts

●Solar energy

●Greenhouses

●Reflected light

●Heat sink

●Radiant energy

●Insulation

Questions

●What is radiant energy? How is it used in a box-type solar oven to heat it up?

●How hot does a typical box-type solar oven get?

●How hot does an oven need to be to cook food?

●Can a solar cooker work on a cloudy day?

●Why use a black cooking pot?

Bibliography

You can find a bunch of alternative solar oven plans on this webpage:

●Solar Cookers International Network. (n.d.). Build a Solar Cooker. Retrieved July 10, 2014.

You can find other information on how solar ovens work and how to use them on these webpages:

●Solar Cookers International Network. (n.d.). Solar Cooking Hint. Retrieved July 10, 2014.

●Aalfs, M. (n.d.). Principles of Solar Box Cooker Design. Solar Cookers International
Network. Retrieved July 10, 2014.

●Sponheim, T. (n.d.). Developing an Intuitive Feel for the Dynamics of Solar Cooking.
Retrieved July 10, 2014.

20

Solar Oven Project

Objective

Follow simple instructions to build a box solar oven from materials like cardboard boxes and
aluminum foil and then improve on the design to build a second, more efficient oven.

Introduction

Many devices have been developed that use solar energy—light and heat emitted from the sun —
including solar panels, artificial photosynthesis, and solar ovens. Solar ovens can cook food,
pasteurize water, or even sterilize instruments using only the power of the sun. How does a solar
oven work? The simple answer is that it is designed to absorb more heat than it releases.

Figure 1, below, shows a picture of the type of efficient, easy-to-build solar oven that you will be
making and testing in this project. The oven is a box within a box. The inner box is covered with a
plastic window (made from a heavy plastic cooking bag available at most grocery stores). The
plastic window works like a greenhouse roof, allowing direct and reflected sunlight to pass into the
inner box, while retaining radiated heat.

Figure 1. This box-type solar oven is both easy-to-build and very inexpensive! (Image credits:

Solar Cookers International Network, 2006)

At the bottom of the inner box, there is a foil-covered shelf, painted black. The shelf serves two
purposes. First, it holds the cooking pot. Second (and more importantly) it acts as a "heat sink."
The shelf absorbs direct and reflected sunlight, which warms it. The shelf then radiates the heat,
and this radiant energy stays mostly trapped in the inner box and warms it. The plastic window
holds the heat in, as does the insulation of the air space (and newspaper) that is between the
inner box and the outer box.

The Procedure section of this project idea gives you step-by-step instructions on building a simple
box-type solar oven. To make this into a complete science fair project, you will need to choose
some aspect of the solar oven design to improve and test. Your choice should be based on your

21

Solar Oven Project

Objective

Follow simple instructions to build a box solar oven from materials like cardboard boxes and
aluminum foil and then improve on the design to build a second, more efficient oven.

Introduction

Many devices have been developed that use solar energy—light and heat emitted from the sun —
including solar panels, artificial photosynthesis, and solar ovens. Solar ovens can cook food,
pasteurize water, or even sterilize instruments using only the power of the sun. How does a solar
oven work? The simple answer is that it is designed to absorb more heat than it releases.

Figure 1, below, shows a picture of the type of efficient, easy-to-build solar oven that you will be
making and testing in this project. The oven is a box within a box. The inner box is covered with a
plastic window (made from a heavy plastic cooking bag available at most grocery stores). The
plastic window works like a greenhouse roof, allowing direct and reflected sunlight to pass into the
inner box, while retaining radiated heat.

Figure 1. This box-type solar oven is both easy-to-build and very inexpensive! (Image credits:

Solar Cookers International Network, 2006)

At the bottom of the inner box, there is a foil-covered shelf, painted black. The shelf serves two
purposes. First, it holds the cooking pot. Second (and more importantly) it acts as a "heat sink."
The shelf absorbs direct and reflected sunlight, which warms it. The shelf then radiates the heat,
and this radiant energy stays mostly trapped in the inner box and warms it. The plastic window
holds the heat in, as does the insulation of the air space (and newspaper) that is between the
inner box and the outer box.

The Procedure section of this project idea gives you step-by-step instructions on building a simple
box-type solar oven. To make this into a complete science fair project, you will need to choose
some aspect of the solar oven design to improve and test. Your choice should be based on your

22

background research, and on the experience gained from building the first oven. Build a second
oven that includes your design improvement, and make measurements to see if you have
improved the oven's performance. You can test your oven by: measuring the internal temperature
with an oven thermometer, or by timing how long it takes to boil a given amount of water in a
cooking pot. Do not worry about the oven catching fire. Paper burns at 233°C (451°F), and your
solar oven will not get that hot.

When you are finished, it would be fun to try using your solar cooker to make a meal. The "Solar
Cooking Hints" webpage listed in the Bibliography, below, has some suggestions. Generally it
takes about twice as long to cook food with a solar oven than in a conventional oven, so you will
need to plan ahead. Rice is a good first dish to try.

Terms and Concepts

●Solar energy

●Greenhouses

●Reflected light

●Heat sink

●Radiant energy

●Insulation

Questions

●What is radiant energy? How is it used in a box-type solar oven to heat it up?

●How hot does a typical box-type solar oven get?

●How hot does an oven need to be to cook food?

●Can a solar cooker work on a cloudy day?

●Why use a black cooking pot?

Bibliography

You can find a bunch of alternative solar oven plans on this webpage:

●Solar Cookers International Network. (n.d.). Build a Solar Cooker. Retrieved July 10, 2014.

You can find other information on how solar ovens work and how to use them on these webpages:

●Solar Cookers International Network. (n.d.). Solar Cooking Hint. Retrieved July 10, 2014.

●Aalfs, M. (n.d.). Principles of Solar Box Cooker Design. Solar Cookers International
Network. Retrieved July 10, 2014.

●Sponheim, T. (n.d.). Developing an Intuitive Feel for the Dynamics of Solar Cooking.
Retrieved July 10, 2014.

23

Materials and Equipment

●Cardboard boxes (4). You will be building two solar ovens, and each oven requires two
cardboard boxes. Here are some notes on picking out two cardboard boxes for making a
single solar oven:

○The inner box should have an opening of at least 38 cm × 38 cm, and be large
enough to hold the cooking pot that you intend to use. It should only be about 2.5 cm
taller than the cooking pot.

○The outer box should be larger all around, with at least 1.5 cm of airspace between
the two boxes on each side. It should also ideally be about 2.5 cm–5.0 cm taller than
the inner box.

○The distance between the two boxes does not have to be equal all the way around.

○Tip: Keep in mind that it is very easy to adjust the size of a cardboard box by cutting
and gluing it.

●Metric ruler or measuring tape

●Straightedge, such as a hard ruler

●Utility knife

●Large sheets of cardboard (2) for making the lid for each of the two solar ovens. Each sheet
must be approximately 8-16 cm larger than the opening of the inner box, when measuring
both dimensions.

●Metal coat hanger. This is to make a prop for the lids.

●Pair of pliers. This is for cutting and bending coat hanger.

●Sheets of cardboard (2) for making the shelf/heat sink for each of the two solar ovens. Each
sheet must be the same size as the bottom of the inner box.

●Sheets of newspaper (several)

●A small roll of aluminum foil

●Black tempera paint (at least 4 oz.). Make sure it is not "washable" tempera paint. This can
be purchased locally at crafts stores or through online suppliers such as Amazon.com.

●Small paint brush

●Elmer's white school glue (at least 8 oz.)

●Reynolds oven cooking bag, "turkey-size", or 47.5 cm × 58.5 cm, or 19" × 23-1/2" (2; you
will need one bag for each of the two solar ovens). Notes on the cooking bag:

○These are available in almost all supermarkets in the U.S.

○They are rated for 204°C (400°F) so they are perfect for solar cooking.

○They are not UV-resistant, thus they will become brittle and opaque over time and
may need to be replaced periodically.

○A sheet of glass can also be used, but this is more expensive and fragile, and does
not offer that much better cooking except on windy days.

24

●For testing your ovens under the same solar conditions, you will need oven thermometers
(2 identical ones) or shallow black cooking pots with covers (2 identical ones). Alternatively,
instead of oven thermometers you could use an infrared thermometer (only 1) with a laser
pointer so you can aim it accurately inside of the solar ovens, such as this one from
Amazon.com.

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools®, Amazon.com,
Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science
Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student
learning. If you have any comments (positive or negative) related to purchases you've made for science
projects from recommendations on our site, please let us know. Write to us at
scibuddy@sciencebuddies.org.

Experimental Procedure

This project follows the

Scientific Method. Review the steps before you begin.

Safety Note: The solar oven you will be building is designed to cook food or boil water. Just like
your kitchen oven, temperatures inside the solar cooker will be high enough to cause serious
burns. Use oven mitts and proper caution to avoid burning yourself. Also, be careful with the utility
knife when cutting cardboard to make the oven.

Building the Solar Oven Base

1. Fold the top flaps closed on the outer box and set the inner box on top. Trace a line around

the base of the inner box onto the top of the outer box, as shown in Figure 2, below.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 2. Set the inner box on top of the (closed) outer box and draw lines around the bottom of

inner box onto the top of the outer box.

25

2. Remove the inner box and, carefully using the utility knife, cut along this line to form a hole

in the top of the outer box, as shown in Figure 3, below.

a. Set aside the outer box for now—you will use it again in step 6.

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 3. Carefully cut along the line you made in step 1 to make the outer box have an opening

that the inner box can fit inside of.

3. Decide how tall you want your oven (the inner box) to be. We recommend about 2.5

centimeters (cm) taller than your largest pot, and about 2.5 cm – 5.0 cm shorter than the
outer box. (Note that you can change the height of the outer box in step 6, below.) This way
there will be a space between the bottoms of the boxes once the cooker is assembled.

4. Carefully use the utility knife to slit the corners of the inner box down to the height you

decided on, as shown in Figure 4, below.

26

Image Credit: Teisha Rowland, Science Buddies / Science Buddies

Figure 4. Cut the corners of the inner box down to the height you want the box to be (based on

step 3).

5. Cut the new, extended flaps completely off so that you are left with a box (without flaps) that

is the height you want your oven to be. To do this, it is easiest to carefully use a
straightedge (e.g., a hard ruler) and the utility knife or a pair of scissors.

a. Set the inner box aside for now — you will not do anything more to it until step 9.

6. If you need to make the outer box shorter, do it now.

a. Remember, you want the outer box to be about 2.5 cm – 5 cm taller than the inner

box.

b. If you need to change the height of the outer box, at each corner measure down to

the new height you want the box to be and then make a mark there, along the box's
edge. Then carefully use a straightedge and the utility knife or a pair of scissors to
cut the box between the marked spots on the edges. You should end up cutting the
box into two pieces as shown in Figure 5, below. Stack the pieces on top of each
other (with one going inside of the other) and tape or glue them back together to
make an intact outer box that is the correct height.

27